Coral bleaching is a serious threat to the world’s reefs and ocean ecosystems as a whole, but scientists have remained suspiciously quiet on the issue. According to a report from the Washington Post, the National Oceanic and Atmospheric Administration has finally broken the silence.

Scientists with the NOAA say that a massive coral bleaching event is occurring throughout the entire world, from Hawaii to the Indian Ocean. Increasing ocean temperatures and acidification could lead to the destruction of over 12,000 square kilometers, or 4,500 square miles, of coral this year alone. Reefs in Hawaii and other North American regions may be hit the hardest, with the event carrying on into 2016.

There are a number of factors contributing to coral bleaching, which is particularly bad in the Pacific. Scientists say global warming, a powerful El Niño year, and a mysterious warm “blob” in the Pacific Ocean are to blame for the damage to coral reefs.

According to Mark Eakin, the head of NOAA’s Coral Reef Watch, “This is only the third time we’ve seen what we would refer to as a global bleaching event, an event that causes mass bleaching in the Indian Ocean, the Pacific Ocean, and the Atlantic-Caribbean basin. [Prior] events were in 1998 and 2010, and those were pretty much one year events. We’re looking at a similar spatial scale of bleaching across the globe, but spanning across at least 2 years. So that means a lot of these corals are being put under really prolonged stress, or are being hit two years in a row.”